The soil moisture monitoring in 2009 was performed without changes in methodology. The Slovak side measured the soil moisture by a neutron probe up to a prescribed depth or to the depth of the ground water level. The Hungarian side measures the soil moisture with a capacity probe to the depth of maximum 3 m. The soil moisture on both sides is expressed by total soil moisture content in volume percentage recorded in 10 cm depth intervals for each measurement during the year. Measurements on the Slovak side were performed on 12 forest monitoring areas, on 5 biological monitoring areas and on 3 agricultural areas – Tab. 5-1. Measurements on the Hungarian side were performed on 6 forest monitoring areas and 8 agricultural areas – Tab. 5-2. The situation of observation objects is shown on Fig. 5-1.

Table 5-1: List of monitoring stations on the Slovak side

Table 5-2: List of monitoring stations on the Hungarian side

 

5.2. Data presentation methods

There were no changes in data presentation methods as well. The soil moisture is presented in figures showing the average soil moisture content in volume percentage for the depth interval from 0 to 100 cm and from 110 to 200 cm. Slight difference is in the Hungarian data presentation, where the value for a depth interval under 110 cm can represent the average value from less than 10 measured values. On colour figures the soil moisture time distribution for the whole measured depth is presented at selected sampling sites. The graphical presentation of the whole set of measured data is given in the Slovak and Hungarian National Annual Reports.

5.3. Evaluation of results on the Hungarian side

In 2009 there were 14 soil moisture measurements done on the Hungarian side. Measurements continued at forestry monitoring sites in the floodplain area and at agricultural monitoring sites in the flood-protected area. Three monitoring sites at forest stands were abandoned, and three new monitoring sites on agricultural area were introduced into the data exchange in 2008 (Fig. 5-1). The moisture conditions of soils are essentially influenced by the rainfall conditions, by the soil layer thickness and its composition, as well as by the ground water level position.

The soil moisture content at the beginning of the vegetation period was higher in comparison with the previous year. Due to the lack of precipitation in April the soil moisture content decreased and the decrease continued till the beginning of June. In June the soil moisture decrease was interrupted thanks to significant amount of precipitation, which resulted in a flood wave at the end of the month. During the flood significant part of the inundation area was flooded; the soil moisture was replenished. The groundwater level was higher by 0.5 m comparing to the previous year. Just after passage of the flood wave, in the first half of July, the maximal soil moisture values were recorded. Since then continuous decrease of soil moisture content followed till the end of vegetation period. Minimal values of soil moisture were registered either at the end of the winter period or at the end of the year (mostly in October). At the end of the year only slight increase of soil moisture values was recorded. Generally it can be stated that the average soil moisture in 2009 was similar or slightly higher in comparison with the previous year.

The soil moisture on forestry monitoring sites

In general, the soil moisture content at all forestry monitoring areas was slightly higher in comparison with the previous year, especially the maximal values were significantly higher thanks to flooding. At the beginning of the vegetation period the soil moisture content reached similar or higher values than in the previous year. Minimal values in the layer to one-meter depth, depending on position of monitoring site, occurred in February (T15), in April (T20), and in October. The minimal values in the layer below one-meter depth occurred mostly in October. Maximal average soil moisture values in the both layers, up to one-meter depth and below one-meter depth were recorded at the beginning of July, just after passage the flood wave. The ground water level all over the year supplied the soil layers on monitoring site T15 (Fig. 5-3), on monitoring sites T16 and T18 it moisturized during increased discharges into the river branch system during May and during the flood wave (Fig. 5-2, Fig. 5-4).

Table 5-3:  The minimal and maximal average soil moisture contents at forestry monitoring sites

The soil moisture on agricultural monitoring sites on the flood protected side

The soil moisture contents at monitoring sites T02, T04, T06 and T12 were mostly dependent on precipitation and weather condition. The ground water level influenced of the soil profile at monitoring site T10, T11 and partially at monitoring sites T02, T03, T04 and T12. During the flood wave the soil moisture content at monitoring site T06 was also influenced by the groundwater. The soil moisture values up to 1 m depth reached high values at the beginning of the vegetation period, but the highest values mostly occurred at the end of June and beginning of July. Average soil moisture values at the beginning of the year were mostly higher then the soil moisture values in the previous year. Minimal soil moisture values in both depth intervals were registered at the end of May and in September and October. The maximal average values in the soil layers below 1 m depth occurred mostly at the end of June and beginning of July as in the upper layer, however at monitoring sites T02 and T12 the maximal average values were registered in August, probably thanks to irrigation. The minimal, average and maximal values were in mostly higher in comparison with the previous year.

Monitoring sites T02, T10, T11 and T12 represent agricultural areas in the Middle and Lower Szigetköz. These monitoring sites have a thick covering layer and throughout the vegetation period the groundwater level moisturised the bottom part of soil layers.

In the inundation area the groundwater moisturised the bottom part of soil layers at monitoring sites T15, T16, T18 and T20. The soil moisture at monitoring site T17 was supplied by groundwater only during the increased discharge in the Danube old riverbed.

Table 5-4:  The minimal and maximal average soil moisture contents at agricultural monitoring sites

 

5.4. Evaluation of results on the Slovak side

Monitoring sites on the Slovak side are situated in the inundation area and flood-protected agricultural area (Fig. 5-1).

The soil moisture at monitoring sites situated behind the derivation channel in the agricultural area (sites No. 2716, 2717, 2718) is stable during the whole observation period. Since the starting of soil moisture monitoring no significant change was observed in the soil moisture content and the position and fluctuation of ground water levels (Fig. 5-5). In the year 2009 the ground water level at monitoring site No. 2716 fluctuated in depths of 2.7-4 m, at site No. 2717 in depths of 2.3-3.4 m and at site No. 2718 in depths of 2-3 m.

The fluctuation of soil moisture content in the depth interval from 0 to 1 m entirely depends on climatic conditions. In the depth from 1 to 2 m, the soil moisture fluctuation is partly influenced by the ground water level, at monitoring area No. 2716 occasionally. The average soil moisture content in the depth up to 1 m in the year 2009 fluctuated in the range from 6 to 22 % at monitoring site No. 2716, in the range from 24 to 35 % at monitoring site No. 2717 and in the range from 27 to 37 % at monitoring site No. 2718. Comparing these values with the previous year it can be stated that the soil moisture content in 2008 was similar. The soil moisture content was supplied during the winter period and especially during rainfalls in March. In April the soil moisture content started to decrease. The decrease was interrupted when the groundwater level increased as a response to the flood wave in June. The minimal values occurred at the end of June and mostly in October. Maximal values were registered at the end of March and in July 2009, after passing the flood wave. In the depth between 1 and 2 m, the soil moisture content mainly varied from 15 to 24 % at monitoring site No. 2716, in the range from 28 to 35 % at monitoring site No. 2717 and in the range from 16 to 34 % at monitoring site No. 2718. Similarly to the upper layer the minimal values were recorded at the end of the year 2009. The maximal values were registered at the end of March and in July, after passing the flood wave.

Table 5-5:  The minimal and maximal average soil moisture contents at agricultural monitoring sites

The soil moisture in the inundation area, along with the ground water level and precipitation, is highly dependent on natural or artificial floods. In the hydrological year 2009 both, artificial and natural flooding of inundation occurred. The highest flow rate reached 8288 m³s^-1, which means that two thirds of inundation area was entirely flooded. The soil moisture content at the beginning of the year was rather low. But thanks to increased precipitation amount in January, February and mainly in March the soil moisture content on most of the observed sites reached maximal average values. Higher values were recorded only just after flooding the inundation area. The lowest values in the layer down to 1 m depth were mostly recorded in September and October. The lowest values in the depth interval from 1 to 2 m were registered almost exclusively at the end of the year, in October and November or December. The maximal values, depending on the position of the monitoring site, occurred after flooding in June and beginning of July. Due to low water level in the Danube during last months of the year the soil moisture content at the end of the year was similar or even lower in comparison with the starting content at the beginning of the year. Concerning the minimal and the maximal values it can be generally stated that minimal values were similar to the values in the previous year, however the maximal values were significantly higher thanks to the flooding.

The thickness of soil profile at monitoring sites No. 2703, 2764, 2763, 2762 and 2761 in the upper part of the inundation area is low, similarly to the Hungarian side. The ground water level at these places fluctuates in the gravel layer only. In 2009 the ground water level on area No. 2703 fluctuated from 1.3 to 5 m, on areas No. 2764, 2763, 2762 and 2761 changed from 0.1-4.7 m. Layers to 1 m depth were highly dependent on climatic conditions, however the flood wave in the Danube in June had a great influence on groundwater level and the soil moisture content (Fig. 5-7). Layers below 1 m depth, except on areas No. 2703 and 2763, were also strongly influenced by the ground water at the time of increased discharge into the river branch system in April-May. Maximal average soil moisture contents occurred at the end of March and after flooding the area in June and beginning of July. Minimal values occurred at the end of the year (mostly in October).

The thickness of the soil profile in the middle part of the inundation area is higher. In general the ground water regime in this region is influenced by the water supply of the river branch system, introduced in May 1993. Moreover, the natural or artificial floods have significant influence on the ground water level. The ground water level in 2009 fluctuated above the boundary between the soil profile and gravel layers - monitoring sites No. 2704, 2705, 2758, 2759, 2760 (Fig. 5-6a, Fig. 5-6b, Fig. 5-8) and supplied the soils with water during the vegetation period. The maximal values of average soil moisture content in the layer down to 1 m depth were reached in June and July 2009, minimal values occurred mostly in September and October 2009. In the layer below 1 m depth the maximal values also occurred in June and July; the minimal values at the end of the year 2009.

Table 5-6:  The minimal and maximal average soil moisture contents at forestry monitoring sites

In the lower part of inundation area, downstream of confluence of the river branch system and the Danube (monitoring sites No. 2706, 2756, 2755), the ground water level usually fluctuates around the boundary between the soil profile and gravel layer. Since the discharges in the Danube in 2009 were rather high the groundwater level moisturised the soil profile. Monitoring sites were flooded at the end of June. Due to riverbed erosion the ground water level fluctuated in the depth between 1 and 4.5 m. The soil moisture in the upper layer in 2009 was mostly dependent on precipitation. Significant refill occurred in February and March, monitoring areas at the end of June and beginning of July were flooded, however since August continuous decrease of soil moisture was characteristic till the end of the year. The minimum and maximum values were related to the minimum and maximum ground water levels respectively. Minimal average values of soil moisture in layers up to 1 m depth occurred at the end of April and in October, in the layer below 1 m depth in November and December. The maximal average values of soil moisture were reached after the flood wave in June and July (Fig. 5-9a, Fig. 5-9b).

The soil moisture contents at monitoring sites No. 2707, 3804, 3805, that are located in the inundation below the confluence of the tailrace canal and the Danube old riverbed, are highly influenced by the flow rate regime in the Danube. The maximum values in 2009, in the depths up to 1 m and between 1 and 2 m, occurred in March, June and July, while the minimum values occurred at the end of the year (October-December). The ground water level at monitoring sites No. 2707, 3804 and 3805 fluctuated in the depth 0-4.0 m. The riverbed erosion negatively influences these monitoring areas. During low flow rates in the Danube the ground water level does not supply the soil profiles sufficiently..